Single-emitter etendue aspect ratio scaler

Abstract

An apparatus emits a laser light beam with a first aspect ratio of etendue R 1 , wherein the optical invariant with respect to a first direction is less than half the optical invariant with respect to a second orthogonal direction. A first cylindrical lens collimates the beam in the first direction. A second cylindrical lens collimates the light beam in the second direction. A bisecting reflective surface has an edge that splits the collimated beam into undeviated and first deviated beam paths. A folding reflective surface redirects the first deviated beam path back toward the bisecting reflective surface, optically parallel with and displaced from the undeviated beam path with respect to the first direction. At least a portion of the redirected first deviated beam path passes the edge and combines with the undeviated path to form an output beam having a second aspect ratio of etendue R 2 not equal to R 1 .

The invention claimed is: 
     
       1. An apparatus for providing a light beam comprising:
 a) a solid-state laser that is energizable to emit, along an optical axis, an input laser light beam that has a first aspect ratio of etendue R 1 , wherein the optical invariant of the input laser light beam with respect to a first direction is less than half the optical invariant of the input laser light beam with respect to a second direction that is orthogonal to the first direction; 
 b) a first cylindrical lens that is disposed to collimate the input laser light beam with respect to the first direction; 
 c) a second cylindrical lens that is disposed to collimate the input laser light beam with respect to the second direction; 
 d) a bisecting reflective surface having an edge that extends along the first direction and that is disposed along the optical axis to split the collimated laser light beam, with respect to the second direction, into an undeviated beam path from light on one side of the edge, and a first deviated beam path from light on the other side of the edge, wherein the undeviated and first deviated beam paths each contain emitted light from the solid-state laser; and 
 e) a folding reflective surface disposed to redirect the first deviated beam path back toward the bisecting reflective surface, so that the redirected first deviated beam path is optically parallel with the undeviated beam path and is displaced from the undeviated beam path with respect to the first direction, 
 wherein at least a first portion of the redirected first deviated beam path passes the edge and combines with the undeviated beam path to form an output beam having a second aspect ratio of etendue R 2  that is not equal to R 1 . 
 
     
     
       2. The apparatus of  claim 1  wherein the folding reflective surface is further disposed to redirect a second portion of the redirected first deviated beam path to the bisecting reflective surface, forming a second deviated beam path that is optically parallel with the first deviated beam path and, with respect to the first direction, is offset from the first deviated beam path. 
     
     
       3. The apparatus of  claim 1  wherein the optical invariant of the input laser light beam with respect to the first direction is less than one fourth of the optical invariant of the input laser light beam with respect to the second direction. 
     
     
       4. The apparatus of  claim 1  wherein the bisecting reflective surface and folding reflective surface are both formed on opposite surfaces of a transparent body. 
     
     
       5. The apparatus of  claim 1  wherein the bisecting reflective surface and folding reflective surfaces are in parallel planes. 
     
     
       6. The apparatus of  claim 1  further comprising a rotationally symmetric lens disposed to direct the output beam toward an optical fiber. 
     
     
       7. The apparatus of  claim 6  wherein the optical invariant of the solid-state laser with respect to the second direction exceeds the optical invariant of the optical fiber. 
     
     
       8. The apparatus of  claim 1  wherein the bisecting reflective surface is formed as a thin film coating and wherein the bisecting reflective surface is disposed at an oblique angle with respect to a normal to the optical axis, wherein the normal lies in a plane that extends in the second direction and includes the optical axis. 
     
     
       9. The apparatus of  claim 4  further comprising a tilt adjusting element that is coupled to the transparent body and defines a tilt axis and wherein rotation about the tilt axis adjusts the displacement in the output beam at least between the redirected first deviated beam path and the undeviated beam path with respect to the first direction. 
     
     
       10. An apparatus for providing a light beam comprising:
 a) a solid-state laser that is energizable to emit, along an optical axis, an input laser light beam that has a first aspect ratio of etendue R 1 , wherein the optical invariant of the input laser light beam with respect to a first direction is less than half the optical invariant of the input laser light beam with respect to a second direction that is orthogonal to the first direction; 
 b) a first cylindrical lens that is disposed to collimate the input laser light beam with respect to the first direction; 
 c) a second cylindrical lens that is disposed to collimate the input laser light beam with respect to the second direction; 
 d) a bisecting reflective surface on one side of a transparent block of material, the bisecting reflective surface having an edge that is disposed along the optical axis to split the collimated laser light beam, with respect to the second direction, into an undeviated beam path from light on one side of the edge, and a first deviated beam path from light on the other side of the edge, wherein the undeviated and first deviated beam paths each contain emitted light from the solid-state laser; and 
 e) a folding reflective surface on an opposite side of the transparent block of material and disposed to redirect the first deviated beam path back toward the bisecting reflective surface, so that the redirected first deviated beam path is optically parallel with the undeviated beam path and is displaced from the undeviated beam path with respect to the first direction, 
 wherein at least a first portion of the redirected first deviated beam path passes the edge and combines with the undeviated beam path to form an output beam having a second aspect ratio of etendue R 2  that is not equal to R 1 . 
 
     
     
       11. The apparatus of  claim 10  wherein the bisecting reflective surface and folding reflective surfaces are in parallel planes. 
     
     
       12. The apparatus of  claim 10  further comprising a rotationally symmetric lens disposed to direct the output beam toward an optical fiber. 
     
     
       13. The apparatus of  claim 12  wherein the optical invariant of the solid-state laser with respect to the second direction exceeds the optical invariant of the optical fiber. 
     
     
       14. The apparatus of  claim 10  wherein the bisecting reflective surface is formed as a thin film coating and wherein the bisecting reflective surface is disposed at an oblique angle with respect to a normal to the optical axis, wherein the normal lies in a plane that extends in the second direction and includes the optical axis. 
     
     
       15. The apparatus of  claim 10  further comprising a tilt adjusting element that is coupled to the transparent block and defines a tilt axis and wherein rotation about the tilt axis adjusts the displacement in the output beam between at least the redirected deviated beam path and the undeviated beam path with respect to the first direction. 
     
     
       16. A method for providing light to an optical fiber, the method comprising:
 a) energizing a solid-state laser to emit light along an optical axis, wherein the light beam has a first aspect ratio of etendue R 1 , wherein the optical invariant of the input laser light beam with respect to a first direction is less than half the optical invariant of the input laser light beam with respect to a second direction that is orthogonal to the first direction; 
 b) collimating the input laser light beam with respect to the first direction through a first cylindrical lens; 
 c) collimating the input laser light beam with respect to the second direction through a second cylindrical lens; 
 d) directing the collimated laser light beam toward a bisecting reflective surface having an edge that is disposed along the optical axis to split the collimated laser light beam, with respect to the second direction, into an undeviated beam path from light on one side of the edge, and a deviated beam path from light on the other side of the edge, wherein the undeviated and deviated beam paths each contain emitted light from the solid-state laser; and 
 e) forming an output beam having a second aspect ratio of etendue R 2  that is not equal to R 1  by disposing a folding reflective surface to redirect the deviated beam path back toward the bisecting reflective surface, so that the redirected deviated beam path is optically parallel with the undeviated beam path and is displaced from the undeviated beam path with respect to the first direction. 
 
     
     
       17. The method of  claim 16  wherein a first portion of the redirected deviated beam path passes the edge of the bisecting reflective surface and a second portion of the redirected deviated beam path is again split by the bisecting reflective surface and is redirected back toward the folding reflective surface. 
     
     
       18. The method of  claim 16  further comprising providing a tilt adjustment to adjust the displacement of the redirected deviated beam path from the undeviated beam path with respect to the first direction. 
     
     
       19. The apparatus of  claim 16  further comprising directing the output beam toward an optical fiber through a rotationally symmetric lens. 
     
     
       20. The apparatus of  claim 16  wherein the bisecting and folding reflective surfaces are formed on opposite sides of a transparent block of material.